1. Field of the Invention
The present invention relates to an image formation apparatus to form images on a recording medium. More particularly, the invention relates to an image formation apparatus using an ink jet recording head to form images by discharging ink or other liquid, and an information processing system using such apparatus as its output means.
2. Related Background Art
An image formation apparatus used together with a computer, word processor or the like, or used individually, such as a copying machine, printer, facsimile apparatus, is provided with a recording head for the formation of images on a recording medium in the form of sheet or others in accordance with image signals applied to driving the head. Also, the image formation apparatuses are roughly divided into those of serial type and line type depending on the scanning methods of recording head to be used. In the meantime, besides the paper sheet, OHP sheet or other plastic sheets usually adopted as recording media, use of other recording media is demanded, as the materials of recording media, including thin paper, processed paper sheet such as for filing use with a perforation or with a roulette or prepared in an arbitrary configuration, and fabrics. Further, with respect to the sizes of recording media, larger ones are increasingly in demand, including sheets for use of advertizement and fabrics for use of making clothes.
Under the circumstances, the ink jet recording method is utilized more as a method suitably usable as output means of information processing systems, such as a printer serving as output terminal of a copying machine, facsimile apparatus, electronic typewriter, word processor, or work station, or a handy or portable printer adopted for use of personal computers, optical disk units, video units, or the like. The ink jet recording method is to record characters, graphic images, and others by discharging fine ink droplets from nozzles. Therefore, this is an excellent method adoptable as means for outputting highly precise images at high speeds. Also, a recording apparatus to which this method is applicable (hereinafter, referred to also as an ink jet recording apparatus) is of a non-impact type, producing lesser noises, while making it easy to perform recording in colors by use of multiple color ink, and to make the apparatus main body smaller, as well as to form images in higher densities, among other advantages. As a result, this method has been in more demand increasingly in recent years. Here, recording is meant to include the provision of ink or the like (setting, image formation, printing, dyeing, and others) for all the ink carriers that accept the provision of ink, such as cloths, threads, paper, or sheet materials. The ink jet recording method is applicable to the wide range of industrial uses, not only for those fields dealing with information processing, but also, for the apparel industries or the like that deal with fabrics, threads, paper, sheet materials or any others that may accept the provision of ink.
With the ink jet method, a liquid jet apparatus (textile printing apparatus, for example) provides a higher degree of flexibility for printing images to be formed, and also, performs textile printing at lower costs, among other advantages, mainly because unlike the screen printing usually practiced, this apparatus does not need any original plate of images to be printed.
Here, in Japanese Patent Application Laid-Open No. 5-212851, there is disclosed one conventional example of a textile printing apparatus using an ink jet recording method. Particularly, as it is clear from the description of FIG. 2 that accompanies this laid-open application, the textile printing apparatus prints by discharging ink from the nozzle head to the textile medium being carried in the direction perpendicular to the head. In other words, ink is discharged from the nozzles in the horizontal direction. Also, for this printing unit that performs ink discharges, there are provided a printing unit having a nozzle head, and a feeding mechanism having an endless belt, each facing the textile medium being carried between them.
Further, for such printing apparatus, it is structured to enable the printing unit to slide horizontally. Here, it is generally practiced that the printing unit is made shiftable, among other arrangements, for the adjustment of the gap formed between the unit and the textile medium or for the replacement of the endless belts.
In the meantime, for the textile printing apparatus using the ink jet recording method described above, it is equally required to enhance the printing speeds as printing apparatuses used for general purposes.
To implement the enhancement of printing speeds, the most direct and realistic method is to increase the number of ink discharge ports of an ink jet recording head, that is, to make the ink jet head longer, even for the structure that should be arranged for printing on fabrics as described above. Such media are formed comparatively long, necessitating a continuous execution of printing More precisely, the number of discharge ports should be increased and arranged in the feeding direction of fabrics or other recording medium (in other words, the ink jet head should be elongated in the feeding direction), thus increasing the width of one line to be printed more by one scanning of the head. Hence, if only the feeding amount is increased accordingly, it is possible to enhance the printing speeds.
However, as the arrangement direction of the discharge ports of the ink jet head is vertical for the textile printing apparatus disclosed in Japanese Patent Application Laid-Open No. 5-212851, the difference in water head between each of the discharge ports becomes larger when making the ink jet head longer. Such difference in water head between each of the discharge ports results in the difference in discharge amounts of the respective nozzles, thus inviting degradation in the quality of printed images in some cases.
On the other hand, there is known the structure wherein a head discharges ink vertically, the so-called downward head arrangement, as disclosed in Japanese Patent Application Laid-Open No. 5-31905, for example. In accordance with this arrangement, the difference in water head does not exist in principle between each of the discharge ports, because the discharge ports are arranged horizontally. Therefore, such problem affecting the image quality unfavorably can be solved.
Moreover, as another effect obtainable by use of the downward head arrangement, recovery processes can be performed uniformly for all the discharge ports by the application of ink suction or other means because of non-existence of difference in water head described above. Also, with this type of arrangement, it is possible to prevent water droplets or the like that may adhere to the discharge port surface from being driven into the interior of the discharge ports.
As a typical image formation apparatus capable of recording on various kinds of recording media as described above, there is one that uses an ink jet recording head to record by discharging ink from its discharge ports. For the image formation apparatus of serial type where the ink jet recording head scans in the direction intersecting the feeding direction of a recording medium to be used, images are recorded totally on the recording medium by repeating such operation that the ink jet recording head is arranged to scan in accordance with image signals, and discharge ink onto a recording medium after having set the medium in a given position, and then, the recording medium is fed at a given pitch subsequent to each recording scan thus performed. Also, for the image formation apparatus of full line type where an ink jet recording head is fixed on the feeding unit of recording media in order to cover the entire width of a recording medium to be used, recording is performed on the entire surface of the recording medium only by the feeding of the recording medium, while arranging the recording head to discharge ink in accordance with image signals when the recording medium is carried in a position opposite to the discharge port surface on which the discharge ports of the ink jet recording head are formed.
The image formation apparatus using an ink jet recording head of the kind tends to present difficulty in performing stable ink discharges due to overly viscous ink brought about by the evaporation of water content in ink in the discharge ports or the gradual creation of ink clogging or the like. To maintain stable ink discharges, therefore, recovery means is provided to remove such difficulty. As recovery means, there is known capping means for minimizing the causes for ink to become overly viscous by capping the discharge port surface of the ink jet recording head while recording is at rest or predischarge means for removing such overly viscous ink by discharging ink as needed, apart from the regular discharges for recording. However, even when the recording head is capped by capping means, it is inevitable that the viscosity of ink advances slowly. Therefore, ink is fed to the recording head by the application of pressure as required so as to forcibly exhaust ink to the interior of capping means. For this purpose, an ink absorbent is provided for capping means or predischarge means for the intended absorption of overly viscous ink exhausted from the recording head. To such absorbent, ink discharged or forced out from the recording head is absorbed.
Further, in Japanese Patent Application Laid-Open No. 6-71897, a recovery method is disclosed, wherein the jet of rinsing liquid is emitted from outside onto an ink jet recording head to clean off ink adhering to the discharge port surface.
However, for the conventional image formation apparatus described above, ink adhering to the discharge port surface is transferred to capping means, and then, the adhesion of ink occurs on it when the discharge port surface of the ink jet recording head is capped with the member that constitutes capping means. Consequently, when a specific ink is used, the water content in ink adhering to the capping means is evaporated due to the change of its chemical properties as the time elapses if the ink is left intact in such condition for a long time. Then, dyes, the main composition thereof, are extracted and deposited on the capping means ultimately. As a result, this extracted substance adheres to the circumference of the ink jet recording head, thus clogging the interior of the discharge ports, or the aperture of capping means when the ink jet recording head is again capped. Further, such extracted substances become nuclei themselves to invite dust particles or dirt in the atmosphere and cause them to adhere to the capping means. Therefore, the contamination of capping means is advances.
The same phenomenon occurs with respect to the absorbent provided for the interior of capping means or predischarge means. In other words, along the evaporation of water content in ink retained in the absorbent, dyes are extracted into the absorbent. By this extracted substance, its ink absorbing function is spoiled after all. A contamination of the kind that concurs in recovery means often deteriorates the recovering capability of an ink jet recording head, and, in turn, the contaminated recovery means invites the adhesion of such contaminated particles to the recording head. Consequently, it becomes impossible to maintain stable discharges of ink after all.
Also, even with the method wherein ink adhering to an ink jet recording head is cleaned off by means of the jet of rinsing liquid emitted onto the discharge port surface, no means is provided for rinsing out the recovery means at all. Therefore, it is impossible to prevent recovery means from being contaminated eventually. The problems described above still remains unsolved when adopting this method effectively for practical use.